1. Field
Example embodiments of the present invention in general relate to a light emitting diode (LED) lighting fixture.
2. Description of the Related Art
High Intensity Discharge (HID) lighting sources are used for a wide array of lighting applications in public spaces such as stores, libraries, theatres and school gymnasiums, for example. An HID lighting fixture typically utilizes a metal halide bulb. For example, FIG. 1 illustrates the use of HID lighting fixtures 100 in one such space, the setting of a big box department store. Typically these fixtures 100 are attached approximately 16 to 25 feet above the surface of the store floor to provide lighting throughout the store.
The Illuminating Engineering Society of North America (IESNA) is the recognized technical authority on illumination and puts out specifications for various types of illumination. The IESNA provides recommendations based on categories and conditions of a particular application or space for brightness, or illuminance. The measurement for illuminance is typically given in foot candles (fc). A footcandle is a unit of illuminance in the foot-pound-second system of units, and represents the illuminance at 1 foot from a 1-candela point source of light. One footcandle is approximately 10.76391 lux (lumens/m2), and in the lighting industry is typically associated as. 1 fc=10 lux.
As an example, the IESNA designates a category A space as a public space, providing examples such as corridors and an ATM key pad, and recommending an illuminance per fixture of 3 fc. Category B areas are spaces where people remain a short time, such as elevators, refrigeration spaces, stairs, etc; the recommended illuminance for a fixture in these spaces is 5 fc. Category C spaces include working spaces with simple visual tasks, i.e., exhibition halls and restrooms. Fixtures in these spaces should have a recommended illuminance of 10 fc.
Category D spaces require a condition for performing visual tasks of high contrast and large size; examples include libraries and museums. The IESNA recommends an illuminance of approximately 30 fc for fixtures in Category D spaces. In spaces requiring a condition for performing visual tasks at high contrast and small size or low contrast and large size (Category E spaces), such as classrooms, food service areas and kitchens, the IESNA recommends a fixture illuminance of approximately 50 fc. A category F space includes school gymnasiums or other areas where visual tasks of low contrast and small size are required. A fixture for a category F space is recommended to have an illuminance of 100 fc. Additionally, there is a category G space, such as an autopsy table or a surgical task, in which the brightness or illuminance is required for visual tasks near a threshold. The IESNA recommends a fixture illuminance of 300 fc for a category G space.
FIG. 2A is a perspective view of a conventional HID lamp fixture employing a metal halide bulb, which is shown in FIG. 2B. Referring to FIGS. 2A and 2B, a conventional HID lamp fixture 100 includes a reflector 110 which is coupled to plug unit 120 that is connected to AC wall plug power, for example. The fixture 100 also includes a ballast 130 which is configured to hold and power metal halide bulb 140.
The HID lamp fixture 100 shown in FIGS. 2A and 2B utilizes a 400 watt metal halide bulb 140 and is configured to receive 436 watts (AC) of wall plug power, to provide a total light output of approximately 15,771 lumens. As noted, HID lamp fixture 100 is a typical lighting fixture used in lighting applications in spaces such as the big box department store shown in FIG. 1, for example.
However, there are several reasons why use of HID lamps are disadvantageous, thus requiring a need for a solid state lighting (SSL) light source to replace the metal halide high bay fixture such as the HID lamp fixture 100 shown in FIGS. 1, 2A and 2B. One concern is the high cost of maintenance. In order to change the metal halide bulb 140 when it goes bad, a lift has to be used along with several people; this adds up to a substantial cost in labor and machinery usage.
Another concern is required warm-up time for the metal halide bulb 140. Typically, it takes approximately 10 minutes for the metal halide bulb 140 to fully warm up to its maximum brightness. Additionally, the metal halide bulb 140 requires a cool down period before the lamp fixture 100 can be turned on again.
A further reason to look to a possible SSL replacement is that for a lighting application as shown in FIG. 1, the metal halide bulb 140 produces a flicker and a slight humming sound when it is energized. The flicker can cause what is known as a stroboscopic effect. The stroboscopic effect makes an object appear to be moving at a rate different than the actual rate at which the object is moving.
Further, metal halide bulbs pose an environmental hazard, in that the bulb materials include mercury. This mercury has to be safely disposed of when the metal halide bulb is no longer usable in fixture 100. Moreover, a typical metal halide bulb's cycle life lasts from about 6,000 to 17,000 hours. However, in order to attain this average life cycle, metal halide manufacturers recommend that the bulb be turned off for about 15 minutes at least once weekly. Accordingly, due to the shortened life and high cost of maintenance, coupled with environmental concerns, the metal halide bulb is not the most efficient and/or cost effective lighting source for many of the categories A-G above, such as the “high bay” lighting application shown in FIG. 1, for example.
LEDs are becoming more widely used in consumer lighting applications. In consumer applications, one or more LED dies (or chips) are mounted within a LED package or on an LED module, which may make up part of a LED lighting fixture which includes one or more power supplies to power the LEDs. Various implementations of LED lighting fixtures are becoming available in the marketplace to fill a wide range of applications. LEDs offer improved light efficiency, a longer lifetime, lower energy consumption and reduced maintenance costs, as compared to HID light sources.